Predicting thermal contact resistance between molten metal droplets and a solid surface

Thermal contact resistance between molten metal droplets (aluminum alloy 380 and bismuth) and solid plates (steel and brass) was measured experimentally. The diameter of the droplets was 4 mm, and droplet impact velocity ranged between I and 3 m/s. Substrate temperature was varied from 25 to 300 degrees C and roughness from 0.06 to 5.0 mu m. Substrate temperature variation under impacting droplets was measured usingJast temperature sensors that had a response time of 40 ns and recorded substrate temperatures at five different radial locations under each droplet. Thermal contact resistance during the first few milliseconds of impact was obtained by matching measured surface temperature variation with an analytical solution of the one-dimensional transient heat conduction equation. An analytical model of the deformation of a free liquid surface in contact with a rough solid was used to calculate the true area of contact between them and, thereby, the thermal contact resistance. Test results agreed well with predictions from the analytical model. Thermal contact resistance values ranged from 10(-7) to 3 X 10(-6) m(2) K/W, increasing with surface roughness and decreasing with rising impact velocity.